I'm new to chickens, but a very old hand at cats. I have always had cats (5-1/2 decades), and done a LOT of cat rescue work over all that time, as well. I know cats. I have also worked with training big cats (lions & tigers), when I was much younger, faster, and not yet physically handicapped.
It doesn't sound at all like a cat.
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Cats don't dig or use holes. They also wouldn't leave only a few feathers and nothing else; you'd find all of the bones, probably the organs (or most of them), and other chicken body parts not too palatable to a cat, unless it was a truly starving cat. You'd know if the cat(s) you saw were that close to starvation. And such starving cats aren't that friendly, either. Besides, cats generally catch birds they can catch or hold in their mouths - although that's not an absolute. Most cats (domestic cats, that is) hunt birds smaller than full-sized chickens. Bantams might be another matter, however, if the cat is a large one. One of my cats - a feral I am still trying to tame & housebreak - catches grackles and similar sized wild birds sideways in her mouth - head sticking out one side of her mouth & feet sticking out of the other side - while they're flying, in mid-air. She just skyrockets up, straight up, like a helicopter, and does triple and quadruple back flips high in the air to position herself relative to the bird in flight, and somehow ends up with them sideways in her teeth. I've seen it hundreds of times, but still can't quite figure out how or what she does. Once the birds' wings are pinned, they are her meals - without fail.
My gut instinct is that your predator is not a cat. Not a domestic cat, that is… can't say for sure if it's a larger cat (bobcat, etc) - although I still doubt even that. Even they leave behind carcass leavings. As do carrion birds who feed on the spot but don't carry the carcass off.